1. Field of the Invention
The present invention relates to a method and apparatus for detecting disordered breathing in a patient and, in particular, to a method and apparatus for detecting patient snoring and/or for dynamically adjusting a snore detection threshold, and to a pressure support system and method of providing pressure support that uses this unique snore detection and/or dynamic adjustment technique to control the pressure provided to a patient.
2. Brief Description of the Prior Art
It is known that may individuals suffer from disordered breathing during sleep. Obstructive sleep apnea (OSA), which is an example of such disordered breathing, is a condition in which sleep is repeatedly interrupted by an inability to breathe due to an obstructed upper airway segment. Obstruction of the airway is generally believed to be due, at least in part, to a general relaxation of the muscles which stabilize the upper airway segment.
Those afflicted with OSA experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of OSA include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Sleep apnea sufferers may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Even if a patient does not suffer from a complete obstruction of the airway, it is also known that adverse effects, such as arousals from sleep, can occur where there is only a partial obstruction of the airway. Partial obstruction can result in shallow breathing referred to as a hypopnea. Other types of disordered breathing are upper airway resistance syndrome (UARS) and vibrations in the airway, such as vibrations of the pharyngeal wall, commonly referred to as snoring. It is known that snoring can accompany closure of the airway leading to UARS, hypopnea, or apnea. Thus snoring provides an indicator that the patient is experiencing abnormal breathing.
It is known to treat such disordered breathing by applying a continuous positive air pressure (CPAP) to the patient's airway. This positive pressure effectively “splints” the airway; thereby maintaining an open passage to the lungs. It is also known to provide a positive pressure therapy in which the pressure of gas produced in the patient's airway varies with the patient's breathing cycle, or varies with the patient's effort, to increase the comfort to the patient. This pressure support technique is referred to a bi-level pressure support, in which the inspiratory positive airway pressure (IPAP) is higher than the expiratory positive airway pressure (EPAP).
It is further known to provide a positive pressure therapy in which a continuous positive pressure is provided to the patient, and where the level of this pressure is automatically adjusted based on the detected conditions of the patient, such as whether the patient is snoring or experiencing an apnea, hypopnea or a change in upper airway resistance. This pressure support technique is referred to as an auto-titration pressure support device, because the pressure support device seeks to provide a pressure to the patient that is only as high as necessary to treat the disordered breathing.
Because, as noted above, snoring is an indicator of a partially collapsed or obstructed airway, with the collapse or obstruction usually occurring in the throat or nasal cavities, a snore detector is used to determine the necessary pressure to treat the patient according to known methods. See, e.g., U.S. Pat. Nos. 5,203,343; 5,458,137 and 6,085,747 all to Axe et al., U.S. Pat. No. 5,259,373 to Gruenke et al., U.S. Pat. Nos. 5,199,424 and 5,245,995 both to Sullivan et al., and U.S. Pat. No. 6,138,675 to Berthon-Jones et al.
Many of these known auto-titration systems having snore detecting capability are susceptible to false snore indications because they do not take into consideration the background noise and other noise in the detecting system. In some cases, the snore detector is equipped with a preset background noise threshold value or preset footprints of a signal corresponding to a snore pressure wave. These preset values are then compared to an electrical representation of the snore pressure wave. However, because the threshold value and footprints are preset, these methods do not take into account dynamic background noise and could erroneously register a false snore.